The long-term goal of this project is to optimize vaccination strategies against influenza. The trivalent subunit influenza vaccine is safe and often effective, but efficacy is reduced in the elderly, who are most susceptible to complications from influenza, or when the vaccine components are not a close match to the circulating viruses. Little is known about the spectra of influenza-neutralizing antibodies produced in humans. The proposed study is to qualitatively and quantitatively examine the antibody specificities induced in an individual by influenza infection or vaccine, the efficiency of producing neutralizing antibodies, and the role these play in antigenic drift. The hypothesis is that in the elderly there is a preponderance of low-specificity, poorly neutralizing antibodies that not only offer poor protection but may allow selection of antigenic variants that are sufficiently robust to become a new epidemic strain. The Specific Aims are: Aim 1: To determine the neutralizing power of individual human antibodies secreted by hybridomas and relate this to their epitope locations and their potential to select escape mutants. Aim 2: To compare the properties of anti-influenza antibodies present in sera of young adult and elderly convalescent or immunized volunteers. Sera will be screened for binding and for inhibitory activity against old and new viruses, and also against a panel of recombinant hemagglutinin and neuraminidase proteins in which antigenic regions are suppressed by substituting novel sequences. Aim 3: To use the well-established mouse hybridoma technology to assist the human antibody studies. Epitopes will be mapped by escape mutant analysis and x-ray crystallography.